The requirements for automatic radar processing and display equipment for shipboard use have not heretofore been successfully met, mostly because of the unique problems posed by the reflection of signals from extended landmasses, and occasionally from waves; these signals tend to dominate and obscure those from the wanted smaller targets, especially other ships, as well as from navigational aids. For example, because of the continuous movement of the ship, the multiple targets produced by landmasses cannot be eliminated by the simple masking techniques that can be used in fixed radar installations, while the large volume of information due to the presence of such landmasses has been considered to make impractical signal processing by computer, which has been used in certain stationary systems for air traffic control, as disclosed, for example, in the Processing of the Eighth Symposium of the A.G.A.R.D. Avionics Panels, London, 21-25 September 1964, particularly at pages 525-556, Chapter 28, Digitalization of Radar Signals and their Evaluation by a Computer for Automatic Tracking of Targets and Chapter 29, Evaluation of Track-while-Scan Computer Logics. See also, U.S. Pat. No. 3,235,867. For these reasons, up to the present time, ship radars have been limited to relatively simple systems whose display is known to be difficult to interpret, especially in time of stress, as when there is danger of collision.
All of these problems are, of course, made more difficult to deal with because of the increasing size of ships, which makes their maneuvering times much greater and greatly extends the distance within which other ships represent a collision danger.